Clinical trials are research studies that are conducted on human beings. In general, these studies are conducted to evaluate what the body does to the drug and what the drug does to the body. In these studies, the efficacy (activity) of the drug and safety and tolerability will be evaluated in the specific patient population. The LGS DISCOVER study (YKP509C003) is evaluating the safety and efficacy of carisbamate in Lennox-Gastaut Syndrome (LGS) patients. There is NO COST to patients who are participating in this study.

The first period of the LGS DISCOVER study is a double-blind placebo-controlled period. That means neither you/your child, nor the study team or investigator will know which treatment is given. This period of the study will compare the investigational drug (carisbamate) to placebo.

Participants who opt to participate in the open-label period will undergo a 2-week double-blind conversion period. The purpose of the conversion is to safely transition participants who are on placebo to carisbamate without revealing what treatments participants were on during the double-blind period.

After completion of the double-blind period of the study (including the conversion period), there is an optional open label (not blinded) extension period. Everyone in the extension period will only receive carisbamate.

For participants who stop treatment early or do not wish to enter the open-label extension period there is a 4-week follow-up period which they will need to complete.

Screening (4 weeks):

The first step is to go through the Informed Consent/Assent process, during which you will learn about the LGS DISCOVER study from the site staff. The goal of this consent/assent process is to make sure you understand the requirements of the study, the possible risks and benefits of participating in the study, and to give you a chance to ask questions. You will receive an Informed Consent/Assent Form to read that explains the study. Signing the forms means you give permission for you or your child to be part of the study. After that, there will be health checks and tests. Participants will continue to take their antiseizure medications (ASMs) during this period and will receive a paper seizure diary that needs to be completed every day.

Double-Blind Treatment (14 weeks):

The seizure diary will be reviewed by the study team. Participants will then be randomly assigned to 1 of the 3 treatment groups. During visits, the seizure diary will be collected, the study drug will be given to participating patients, and health checks and tests will be done.

Double-Blind Conversion Period (2 weeks):

Patients who complete the double-blind treatment period will have the opportunity to enter the open-label extension period. Participants will enter a 2-week double-blind conversion period. During this 2-week period, participants will be transitioned to carisbamate. At the end of this 2-week period, all patients will continue on carisbamate during the open-label extension period.

Open-Label Extension (at least 52 weeks):

All participants will receive the study drug, carisbamate. Clinic visits will occur monthly for the first 3 months then every 3 months thereafter or as needed.

Follow-Up (4 weeks):

Participants who stop treatment early or decide not to enter the open-label extension study will need to attend an end of study visit. After this, the dose of the study drug will be reduced gradually over 2 weeks. There will be a further follow-up visit 2 weeks after the final dose of study drug. During this follow-up visit, health checks and tests will be done.

Participants will be randomly assigned to one of three study treatment groups:

Neither the participants nor the study team/investigator will know who is in which study treatment group.

All participants will continue to take their antiseizure medications (ASMs) throughout the study.

All participants will receive the study drug, carisbamate. During this time, dosage of carisbamate and/or antiseizure medications (ASMs) may be adjusted as needed. The maximum dose of carisbamate will be 300 mg twice a day or pediatric equivalent (based on patient weight).

Additionally, once the 52-week open-label extension period is completed, the patient may have the opportunity to continue to receive carisbamate. If you are eligible, carisbamate will be provided to you as part of an Expanded Access Study without entering the Follow-up Period or in a continuation of the open-label extension period.